1. Field of the Invention
The present invention relates to a thin-film magnetic element including hard magnetic layers for orienting the magnetization direction of at least one magnetic layer included in a multilayer film having magnetoresistance and a manufacturing method thereof. In particular, the present invention relates to a thin-film magnetic element capable of effectively orienting the magnetization direction of the magnetic layer and a manufacturing method thereof.
2. Description of the Related Art
FIG. 20 is a sectional view of a conventional thin-film magnetic element viewed from the air-bearing surface (ABS).
A spin-valve thin-film element formed such that an antiferromagnetic layer 2 provided on an underlayer 1 extends toward both sides in the X direction and that the center of the antiferromagnetic layer 2 protrudes by a height of d1. The protruding antiferromagnetic layer 2 is provided with a pinned magnetic layer 3, a nonmagnetic conductive layer 4, a free magnetic layer 5, and a protective layer 6, forming a multilayer film 7, which is a laminate including the underlayer 1 to the protective layer 6.
In the thin-film magnetic element shown in FIG. 20, the antiferromagnetic layer 2 is a platinum-manganese (Ptxe2x80x94Mn) alloy film.
The pinned magnetic layer 3 and the free magnetic layer 5 are formed of a nickel-iron (Nixe2x80x94Fe) alloy, cobalt (Co), an iron-cobalt (Fexe2x80x94Co) alloy, an Fexe2x80x94Coxe2x80x94Ni alloy, or the like. The nonmagnetic conductive layer 4 is formed of a nonmagnetic conductive material having a low electrical resistance such as copper (Cu).
Bias underlayers 8 serving as a buffer layer and an oriented film is formed of chromium (Cr) or the like so as to extend on the antiferromagnetic layer 2 toward both sides in the X direction and along both side surfaces of the multilayer film 7. Providing the bias underlayers 8 allows a bias magnetic field generated from hard bias layers 9, which are hard magnetic layers and will be described below, to be increased.
The bias underlayers 8 are provided with the hard magnetic layers 9 formed of, for example, a Coxe2x80x94Pt alloy or a Coxe2x80x94Crxe2x80x94Pt alloy thereon.
The hard bias layers 9 are magnetized in the X direction, or track width direction, in the drawing. The bias magnetic field from the hard bias layer 9 orients the magnetization of the free magnetic layer 5 in the X direction.
The hard magnetic layers 9 are provided with interlayers 10 formed of a nonmagnetic material such as tantalum (Ta) thereon. The interlayers 10 are provided with electrode layers 11 formed of chromium (Cr), gold (Au), tantalum (Ta), tungsten (W), or the like thereon.
As described above, the bias underlayers 8 are formed so as to extend on the antiferromagnetic layer 2 toward both sides in the X direction and along both side surfaces of the multilayer film 7, and thereby the bias magnetic field generated from the hard bias layers 9 is increased.
The hard bias layers 9, which are formed to orient the magnetization of the free magnetic layer 5, are required to generate a large bias magnetic field near the free magnetic layer. However, the conventional thin-film magnetic element is formed, as shown in FIG. 20, such that the bias underlayers 8 taper off on both sides of the multilayer film 7, thus being scarcely deposited on both sides of the free magnetic layer 5. Therefore it is difficult to increase the bias magnetic field generated from the hard bias layers 9, or the hard magnetic layers.
Accordingly, an object of the present invention is to provide a thin-film magnetic element capable of increasing a bias magnetic field generated from hard magnetic layers, having bias underlayers with a sufficient thickness at a free magnetic layer. The bias underlayers are formed so that sidewall portions thereof have a thickness larger than that of base portions thereof.
To this end, according to one aspect of the present invention, there is provided a thin-film magnetic element comprising a substrate and a magnetoresistive multilayer film including at least one magnetic layer, provided on the substrate. Bias underlayers formed of a nonmagnetic material are comprised, having sidewall portions formed along side surfaces of the multilayer film and base portions formed on the surface of the substrate in the track width direction. The thickness of the sidewall portions is larger than that of the base portions. Hard magnetic layers for orienting the magnetization direction of at least one magnetic layer are deposited on the bias underlayers at sides of the multilayer film.
Forming the sidewall portions with a thickness larger than that of the base portions can result in the substantially uniform thickness of the sidewall portions. The bias underlayers are formed with a sufficient thickness near at least one free magnetic layer. Thus, the coercive force and the remanence ratio of and the bias magnetic field from the hard magnetic layers can be increased, and therefore Barkhausen noise of the thin-film magnetic element can be decreased.
The bias underlayers may be formed of at least one nonmagnetic material selected from Cr, W, Mo, V, Nb, and Ta.
Preferably, the sidewall portions of the bias underlayers have a thickness in the range of 15 to 75 xc3x85. If the thickness of the sidewall portions is less than 15 xc3x85, the hard magnetic layers cannot sufficiently generate a bias magnetic field on the sidewall portions. If the thickness of the sidewall portions is more than 75 xc3x85, the bias underlayers block the bias magnetic field generated from the hard magnetic layers, and consequently the orientation of magnetization of the free magnetic layer becomes difficult.
The base portions of the bias underlayers preferably have a thickness in the range of 15 to 50 xc3x85, advantageously increasing the coercive force and the remanence ratio of the hard magnetic layers.
The bias underlayers preferably have a body-centered cubic crystal structure of which the {200} faces are oriented parallel to the interfaces between the base portions thereof and the hard magnetic layers. Further, the hard magnetic layers may have a hexagonal close-packed crystal structure of which the {100} faces are oriented parallel to the surface of the magnetic layer of which the magnetization direction is oriented by a bias magnetic field from the hard magnetic layers.
When the bias underlayers have a body-centered cubic structure, and the {200} faces of the structure are oriented parallel to the interfaces between the base portions and the hard magnetic layers, the hard magnetic layers have a hexagonal close-packed structure of which the {100} faces are oriented parallel to the interfaces between the base portions and the hard magnetic layers. When the {100} faces are oriented parallel to the interfaces between the base portions and the hard magnetic layers, the {100} faces can be oriented parallel to the surface of the free magnetic layer. Thus, the c axes of the crystal axes of the hard magnetic layers are oriented parallel to the surface of the free magnetic layer, so that the bias magnetic field is generated effectively. Also, the coercive force and the remanence ratio of the hard magnetic layers are increased. As a result, the Barkhausen noise of the thin-film magnetic element is lowered and the sensitivity of magnetic field detection is improved.
The multilayer film may comprise an antiferromagnetic layer, a pinned magnetic layer of which the magnetization direction is pinned by the antiferromagnetic layer, a nonmagnetic material layer, and a free magnetic layer of which the magnetization direction is changed by an external magnetic field. The hard magnetic layers are provided at both sides of the free magnetic layer in the track width direction, and thereby the magnetization of the free magnetic layer is oriented in the direction which intersects the magnetization direction of the pinned magnetic layer by magnetic coupling with the hard magnetic layers. Thus the magnetic element results in a so-called spin-valve thin-film magnetic element.
Preferably, at least at each side of the free magnetic layer in the track width direction, the sidewall portions have, a thickness larger than that of the base portions.
Pursuant to another aspect of the present invention, there is provided a method of manufacturing a thin-film magnetic element. The manufacturing method comprises:
(a) providing a magnetoresistive multilayer film on a substrate;
(b) providing a lift-off resist layer having incisions at the undersurface thereof on the multilayer film;
(c) removing the multilayer film at portions which are not covered with the lift-off resist layer;
(d) depositing bias underlayers on sides of the multilayer film and on the substrate at a predetermined angle with respect to the normal to the substrate, wherein sidewall portions of the bias underlayers deposited along the sides of the multilayer film have a thickness larger than that of base portions deposited on the surface of the substrate;
(e) depositing, on the bias underlayers, a hard magnetic layers for orienting the magnetization direction of at least one magnetic layer included in the multilayer film;
(f) providing electrode layers on the hard magnetic layers;
(g) removing the resist layer; and
(h) magnetizing the hard magnetic layers in the track width direction.
In step (d), by forming the bias underlayers on the sides of the multilayer film and on the substrate at a predetermined angle with respect to the normal to the surface of the substrate, the sidewall portions formed can have a thickness larger than that of the base portions.
The sidewall portions with a thickness larger than that of the base portions can have a substantially uniform thickness, allowing the bias underlayers to have a sufficient thickness near at least one magnetic layer included in the multilayer film. Thus, the coercive force and the remanence ratio of and the bias magnetic field from the hard magnetic layers can be increased, and therefore Barkhausen noise of the thin-film magnetic element can be decreased.
Preferably, in step (c), the multilayer film is provided so that the angle between the surface of the substrate and each side of the multilayer film is in the range of 20 to 60xc2x0. The bias underlayers are deposited at a predetermined angle in the range of 30 to 60xc2x0 in step (d). Thus, the sidewall portions can be formed with a thickness larger than that of the base portions.
In step (c), the multilayer film may be provided so that the angle between the surface of the substrate and each side of the multilayer film is in the range of 20 to 45xc2x0, and the bias underlayers are deposited at a predetermined angle in the range of 19 to 60xc2x0 in step (d). The multilayer film may be provided so that the angle between the surface of the substrate and each side of the multilayer film is in the range of 20 to 30xc2x0, and the bias underlayers are deposited at a predetermined angle in the range of 15 and 60xc2x0 in step (d).
Preferably, in step (d), the bias underlayers are deposited by sputtering selected from among ion-beam sputtering, long-throw sputtering, and collimation sputtering.
Preferably, in step (e), the hard magnetic layers are deposited by sputtering selected from ion-beam sputtering, long-throw sputtering, and collimation sputtering.
The bias underlayers may be formed of at least one nonmagnetic material selected from Cr, W, Mo, V, Mn, Nb, and Ta.
Preferably, in step (d), the sidewall portions are deposited with a thickness in the range of 15 to 75 xc3x85. Also, the base portions are deposited with a thickness in the range of 15 to 50 xc3x85.
The bias underlayers may be deposited at a predetermined angle of 50xc2x0 or more in step (d) so as to have a body-centered cubic crystal structure of which the {200} faces are oriented parallel to the interfaces between the base portions thereof and the hard magnetic layers.
When the bias underlayers have a body-centered cubic structure, and the {200} faces of the structure thereof are oriented parallel to the interfaces between the base portions and the hard magnetic layers, the hard magnetic layers may be deposited in step (e) so as to have a hexagonal close-packed crystal structure of which the {100} faces are oriented parallel to the surface of the magnetic layer of which the magnetization direction is oriented by a bias magnetic field from the hard magnetic layers.
The multilayer film may be formed in step (a) so as to comprise an antiferromagnetic layer, a pinned magnetic layer of which the magnetization direction is pinned by the antiferromagnetic layer, a nonmagnetic material layer, and a free magnetic layer of which the magnetization direction is changed by an external magnetic field. The hard magnetic layers are provided at both sides of the free magnetic layer in the track width direction, and thereby the magnetization of the free magnetic layer is oriented in the direction which intersects the magnetization direction of the pinned magnetic layer by magnetic coupling with the hard magnetic layers. Thus the magnetic element results in a so-called spin-valve thin-film magnetic element.
In step (d), at least at both sides of the free magnetic layer in the track width direction, the sidewall portions preferably have a thickness larger than that of the base portions.
According to the present invention, forming the bias underlayers such that the sidewall portions thereof have a thickness larger than that of the base portions thereof and forming the hard magnetic layers on the bias underlayers allow the sidewall portions have an uniform thickness. Also, the bias underlayers can have sufficient thickness near at least one magnetic layer included in the multilayer film.
Thus, the coercive force and the remanence ratio of and the bias magnetic field from the hard magnetic layers can be increased, and therefore Barkhausen noise of the thin-film magnetic element can be decreased.